Fuse structures formed of concentric fuse tubes to provide a maximum heat radiating surface and a novel venting means



May 17, 1966 F. 1.. CAMERON PROVIDE FUSE STRUCTURES FORMED OF CONCENTRIC FUSE TUBES TO A MAXIMUM HEAT RADIATING SURFACE AND A NOVEL VENTING MEANS Filed Oct. 10, 1963 2 Sheets-Sheet 1 Fig.4. Fig.5.

ATTORNEY INVENTOR Frank L. Cameron \iJgI/EVESSES V 5% May 17, 1966 F. L. CAMERON PROVIDE FUSE STRUCTURES FORMED OF CONCENTRIC FUSE TUBES TO A MAXIMUM HEAT RADIATING SURFACE AND A NOVEL VENTING MEANS 2 Sheets-Sheet 2,

Filed Oct. 10. 1963 Fig.7.

United States Patent FUSE STRUCTURES FORMED 0F CONCENTRIC FUSE TUBES T0 PROVEDE A MAXHMUM HEAT RADIATIN G SURFACE AND A NOVEL VENTING MEANS Frank L. Cameron, North Huntingdon Township, Irwin, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 10, 1963, Ser. No. 315,304 6 Claims. (Cl. 200120) This invention relates to fuse structures in general, and, more particularly, to improved fuse structures having a novel venting means associated therewith and thereby capable of providing considerable heat-radiating surfaces.

A general object of the present invention is to provide an improved and highly efficient fuse structure in which novel venting means are incorporated therewith, so that the fuse-element cross-sectional area may be considerably reduced.

As well known by those skilled in the art, in a currentlimiting fuse, the ratio of full-load current to let-through current should be as great as possible. This means that for a given material, the fuse element cross-section should be as small as practicable, so that the element will be most rapidly melted under the steep rate of current rise of a fault condition. The present invention is particularly concerned with limiting the element cross-sectional area by providing a fuse construction which offers a maximum heat-radiating surface.

Another object of the present invention is to provide an improved current-limiting fuse having the form of an annulus. Still a further object of the present invention is to provide an improved vented fuse construction capable of rapid assembly and adapted to economical manufacture. Still a further object of the present invention is to provide an improved fuse structure of annular configuration susceptible for use with a widevariety of different fusible elements.

Another object of the present invention is to provide an improved current-limiting fuse particularly adapted to utilize strap-like fusible elements, such as those set forth in United States patent application filed January 30, 1961, Serial No. 85,872 by Frank L. Cameron entitled Fuse, and assigned to the assignee of the instant application which issued May 26, 1964 as US. Patent 3,134,874.

Still a further object of the invention is to provide an improved current-limiting fuse in the form of an annulus in which the length of the fusible elements may be the same by a novel mounting means.

Additional objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in which:

FIG. 1 is a longitudinal sectional view taken through a fuse structure incorporating the principles of the present invention;

FIG. 2 is a fragmentary top plan view of the fuse structure of FIG. 1;

FIG. 3 is a side elevational view of a notched fusible element which may be used in the fuse structure of FIG. 1;

FIG. 4 is a top plan view of the notched fusible element of FIG. 3;

FIG. 5 is a side elevational view of a further form of fusible element, which may be utilized in the fuse construction of FIG. 1;

FIG. 6 fragmentarily illustrated a modified form of fuse construction, generally similar to that of FIG. 1, but employing only a fusible means supported by the inner fuse tube of FIG. 1;

FIG. 6A is a fragmentary view of a different type of fuse orientation than that used in FIGS. 1 and 2;

FIG. 7 is a modified form of fuse structure, the figure being taken longitudinally and sectionally therethrough;

FIG. 8 is a detail plan view of one of the end annular terminal discs of the modified fuse structure of FIG. 7; and,

FIG. 9 is a side view of one of the strap-like fusible elements utilized in the modified fuse construction of FIG. 7.

With reference to the drawings, and more particularly to'FIGS. 1 and 2 thereof, the reference numeral 1 generally designates a fuse structure of ring shape, or annular form, having an axial venting passage 2 extending therethrough. Generally, the fuse structure 1 comprises a pair of concentrically-arranged insulating fuse tubes 3, 4 constructed of a suitable insulating material of the requisite strength, such as glass-melamine material. For certain purposes, however, a gas-evolving material, such as fiber, or a high-molecular-weight polyoxymethylene material, such as that set forth in Gainer et al. US. Patent 3,059,081 may be used.

As shown in FIGS. 1 and 2, the concentrically-related insulating fuse tubes 3, 4 are fixedly secured into position by apair of metallic end caps 5, 6. The end caps 5, 6 maybe of any desired construction, but are preferably of one-piece construction and silver plated over the entire surface. The end caps 5, 6 may be secured to the fuse tubes 3, 4 by any suitable means, but preferably are pressed over the tubes 3, 4, and cemented into place to provide a strong fully-sealed assembly.

I Situated between the inner surfaces 5a, 6a of the end ferrules 5, 6 and the adjacent ends of the fuse tubes 3, 4 is a pair of ring-shaped terminal plates 7, 8, to which one or more fusible elements 10 may be connected. As a result, the annular terminal plates 7, 8 .are in conductive relation with respect to the end annular terminal ferrules 5, 6, and provide a convenient means for connecting the several fusible elements 10, when a plurality of such elements are required for the particular current rating of the fusible device 1.

As shown in FIG. 1, the confronting inner faces 3a, 4a are preferably helically grooved, as at 3b, 4b, to accommodate one or more helically-arranged fusible elements 10, which may be of the type illustrated in FIGS. 3 and 4 of the drawings.

It is desirable to have the several fuse elements 10 of equal length. To accomplish this end, the pitch of the groove cut in the outer tube is greater than that of the groove cut in the inner tube so that the elements may be of equal length despite the different mean diameters on which they are wound.

As shown in FIGS. 3 and 4, the fusible elements 10 may be formed of any suitable fusible material, such as silver, for example, and may have, for instance, notches 10a spaced axially therealong to provide thereby a current-limiting function. Reference may be had to United States Patents 2,496,704, issued February 7, 1950 to H. H. Fahnoe and 2,502,992 issued April. 4, 1950 to H. L. Rawlins and H. H. Fahnoe for the theory of operation of the fusible elements 10. It is, however, to be clearly understood, that the present invention is not restricted to any particular type of fusible element, and the fusible element of FIGS. 3 and 4 is illustrated merely by way of example, andnot by way of limitation.

Another type of fusible element, which may be utilized in the fuse structer 1, for certain applications is, that illustrated in FIG. 5 of the drawings, and designated by the reference numeral 12. As shown in FIG. 5, the fusible element 12 is of round, or rod-like configuration, and may have a plurality of annular notches 12a spaced axially therealong for a current-limiting function.

From the foregoing description it will be apparent that the fusible elements 10, 12 may be positioned within the helically-arranged grooves 3b, 4b, and thereby held in a relatively fixed position. Preferably, suitable filler means, such as a granular filler 13, such as sand, is disposed in the annular space 14 provided between the two concentric fuse tubes 3, 4. As well known by those skilled in the art, the sand 13 has a desirable arc-extinguishing function during fuse operation. I For certain applications, it may be desirable to' provide a fusible element only on one of the two fuse tubes 3, 4, and FIG. 6 fragmentarily illustrates such a modified type construction. As shown in FIG. 6, the fuse element 10 is omitted from the wall of the outer fuse tube 4, and only the inner fuse tube 3 contains the grooves 3b.

As will be obvious, the grooves 3b, 4b may not only assume a helical configuration as illustrated in FIGS. 1

and 2, but may also extend axially of the fuse structure 1 in direct alignment with the end terminal discs 7, 8, as illustrated in the fragmentary fuse construction shown in FIG. 6A of the drawings.

FIG. 7 illustrates a modified type of fuse structure 20, which is particularly adapted to accommodate a ribbonlike, or strap-like fusible element 21, such as set forth and claimed in US. patent application Serial No. 85,872 referred to hereinbefore.

Each fusible element 21 is ribbon-like in form and preferably comprised of silver. The ribbon 21 is segmented by V-notching on both edges periodically along its length to provide a series of restricted areas, which fuse to provide a series of arcs, the summation of which provides a high arc voltage, as is known in the art. For

example, in a fuse element 21 the width thereof may be A inch with .005 inch thickness. The V-notches may have an included angle of about 36 at /1 inch intervals along its length.

As shown in FIG. 9, the fusible element 21 is preferably prebent, or preindexed and assumes a zig-zag appearance. Each successive bend is preferably equal and opposite to the adjacent bends relative to a central axis along the fusible element.

Investigations with non-indexed ribbon-type fusible elements have shown that expansion and contraction of fusible element effected pronounced flexing at one or two points along the lines of the fuse, ultimately causing the fuse to fracture under fatigue failure.

Preindexing of the fusible element 21 as shown in FIG. 9, effects uniform distribution of the flexing among the various indexed points, with the result that variation in stress intensity at any one point is kept within the endurance range of the metal, and the element 21 does not break. As an example of fatigue proofing of the fusible element 21 through prebending or preindexing, as shown in FIG. 9, a silver strap of the type hereindescribed, having a length of ten inches, was indexed at about A inch intervals to an included angle of about 120 resulting in a fuse having fatigue-proof elements.

To assist in supporting the several fusible elements 21 in the modified-type fuse construction 20, of FIG. 7 there is preferably provided a pair of spaced radially-slotted terminal discs 24, having'registered radial slots 24a, 24b 25a, 25b provided therein. As shown in FIG. 8, the ends of the fusible elements 21 are looped over the radial slots in one terminal disc, and are soldered to the outer face of the other radially-slotted terminal disc. The result is a fusible connection between the ring-shaped radially-slotted terminal discs 24, 25.

Preferably, each of the ring-shaped terminal discs 24, 25 has a metallic stud 28 associated therewith, and terminal bolts 30 are secured in the tapped openings 28a of the terminal studs 28. This has the advantage of securely fastening the end conducting annular ferrules 34, in

- position.

isaid patent application Serial No. 85,872. Such an indicator assembly 37 preferably employs an indicator plug 40, which is biased by a compression spring 41 to an external indicating position. The indicator plug has an eyelet 43, through which a fusible conductor 31 of I structure 20 to assist in arc extinction.

From the foregoing description it will be apparent that there is provided a novel vented-type fuse structure 1, 20 which has particular applicability to current-limiting typesv of fuses. As well known by those skilled in the art, in a current-limiting fuse the ratio of full-load current to let-through current should be as great as possible. This means that for a given material, the fuse-element cross-section should be as small as practicable, so that the element will be most rapidly melted under the steep rate of current rise of a fault condition. The fuse structure set forth in the present invention provides a maximum heat-radiating surface, and thereby permits a limitation of the fuse element cross-sectional area.

It is apparent that with the construction set forth in FIGS. 1 and 2 the fuse elements 1f) being wound on the tube walls with themselves, and with the hollow core providing an axial venting passage 2, the resulting fuse construction 1 providesa significant additional radiating surface and there will be a very good dissipation of the internally-generated heat of the fuse. 7

Although there have been illustrated and described specific structures, it is to be clearly understood that the same were merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art without departing from the spirit and scope of the invention.

I claim as my invention:

1. A fuse structure of annular form having an axial venting passage therethrough comprising, in combination, a pair of concentrically-arranged insulating fuse tubes having an annular space therebetween, generally annular terminal means each having a central opening and enclosing the opposite ends of the annular space between said concentically-arranged fuse tubes, generally helical groove means on the confronting inner faces of both of said fuse tubes, and a fusible element disposed in each of said groove means and electrically connecting said terminal means, the pitches of said groove means on said fuse tubes being different to provide equal lengths of the associated fusible elements.

2. In combination, a fuse structure forming an annulus and having an axial venting passage therethrough, said fuse structure including a pair of concentrically-arranged, insulating fuse tubes having an annular space therebetween, a granular arc-extinguishing filler material disposed within said annular space, a pair of generally annularly-shaped end ferrule caps each having a central opening and enclosing the opposite ends of the annular space between the fuse tubes, generally helical groove means on the inner faces of both of said fuse tubes and fusible means disposed in each of the groove means and extending through said granular arc-extinguishing filler material electrically connected to said end ferrule caps, the pitches of said groove means on said fuse tubes being different to provide equal lengths of the associated fusible elements.

3. In combination, a fuse structure forming an annulus and having an axial venting passage therethrough, said fuse structure including a pair of concentrically-arranged fuse tubes having an annular space therebetween, a pair of spaced ring-shaped terminal discs disposed adjacent the ends of said annular space, a granular arc-extinguishing filler material disposed within said annular space, a pair of annularly-shaped end ferrule caps disposed at the opposite ends of the fuse tubes to enclose the opposite ends of the annular space between the tubes, each of said end caps having inner and outer surfaces extending axially along the fuse tubes toward the other end cap and being pressed on said fuse tubes and cemented in place, and fusible means extending through said granular arc-extinguishing filler material electrically connected to said end ferrule caps.

4. The combination of claim 3, wherein the spaced ring-shaped terminal discs have radial slots provided therein, and the fusible means extends through the slots in the terminal discs.

5. A vented fuse comprising annular insulating casing means including a pair of concentrically disposed, spaced tubes, spaced terminals disposed at opposite ends of the annular insulating casing means, said annular casing means defining an annular arc-extinguishing chamber, fusible means disposed within said annular arc-extinguishing chamber and electrically interconnecting said spaced terminals, a filler of granular material disposed within said chamber in immediate proximity to the fusible means, whereby blowing of the fusible means during fuse operation will result in a cooling action by said granular material on the established arc and a pair of annularly shaped end ferrule caps each having a central opening to form with one of the tubes an axial vent passage through the fuse, said end caps being disposed at the opposite ends of the tubes to enclose the opposite ends of the space therebetween, each of said end caps having inner and outer surfaces extending axially along the fuse tubes toward the other end cap and being pressed on said tubes and cemented in place.

6. The combination according to claim 5, wherein said casing means has a grooved surface on at least one of the tubes facing the arc-extinguishing chamber to hold the fusible means.

References Cited by the Examiner UNITED STATES PATENTS 1,011,232 12/1911 Muller. 1,855,086 4/1932 Bladholm 200125 2,879,354 3/1959 Fahnoe 200 X 2,898,425 8/1959 Simmons 200313 3,011,038 11/1961 Smith 200131 X FOREIGN PATENTS 319,749 12/ 1930 Great Britain.

BERNARD A; GILHEANY, Primary Examiner. 

5. A VENTED FUSE COMPRISING ANNULAR INSULATING CASING MEANS INCLUDING A PAIR OF CONCENTRICALLY DISPOSED, SPACED TUBES, SPACED TERMINALS DISPOSED AT OPPOSITE ENDS OF THE ANNULAR INSULATING CASING MEANS, SAID ANNULAR CASING MEANS DEFINING AN ANNULAR ARC-EXTINGUISHING CHAMBER, FUSIBLE MEANS DISPOSED WITHIN SAID ANNULAR ARC-EXTINGUISHING CHAMBER AND ELECTRICALLY INTERCONNECTING SAID SPACED TERMINALS, A FILLER OF GRANULAR MATERIAL DISPOSED WITHIN SAID CHAMBER IN IMMEDIATE PROXIMITY TO THE FUSIBLE MEANS, WHEREBY BLOWING OF THE FUSIBLE MEANS DURING FUSE OPERATION WILL RESULT IN A COOLING ACTION BY SAID GRANULAR MA- 